Suppression system



July 29, 1952 H. c. STORCK SUPPRESSION SYSTEM 2 SHEETSSHEET 1 Filed Sept. 20, 1944 M TEQSQ w f w W @WMPMM/i way/ mar BY M A E/A 5 ADV/94%) July 29, 1952 H. c. STORCK SUPPRESSION SYSTEM 2 SHEETS-SHEET 2 Filed Sept. 20, 1944 INVENTOR. #MMMJ/m/ |'I||| i I i t l ||||L rlllillklllllulllll Patented July 29, 1952 UNITED (Granted Sunder; the act of March 3,1883, ,as.

amended "April-30;; 1928;"370fOFGI-757) The invention described-. herein may, be \manu-w factured. and fused. by or .for. the Government for. governmental purposes;without thei'payment to, me .of,anyroya1ty thereon-j Thisinvention relatesito'. electronic suppression 5 circuits; having ,fori an objectv the suppression ,of

a radio receiver; over v.a .subs'tantia1.,,p0rtion of a; redeived vpulseisignal cyc1e.-

Another.object-.is touprQvide, for a radio receivers. having, a '-ic'athode my; oscilloscope as. an output indicating, device a means forobliteratinghoise I from thecathoderay tube. screen durin'gthe above statetctperiodh V A? further, object, is to. provide means .for. p110 IongingQthe' eff eetsxof a blanking pr. similar. pulse.

A; furth'en obje'ctjis 1 to. provide means.- for in: creasing thei durationor 1 width).-.'. of. the pulsfei supiiliedffrom a h ghlimpedancel source, and for varying. the ,duration,,ofsuccessive pulses transm iatjedthefein'.

A itirth ,objectis to. providemuls'e. coupiing f between gcir'cuitv networks of difierent impedance. characteristics;

Another, obj eet: i's.1to,pro.v.ideitriggeringmeans in an; electronic ,circuit. so that. said circuit. will" trigger {from .sourcesof different output, impedeanee nva'lue's or, .of .fdiff'rentv pulse tvolta'ge .amplil, nudes, and whichwillitrigger ,with pulses of Widely; difieiientnurations.

A. further object is to prevent thiuncontroliablej blo'cking pf a receiver by a transmitted.signal'by rendering the, receiver insensitive .at th ,time,,ofl..if occurrence of the transmitted signal.

A stilljfurther obj ect, is to ,var'iab1y',contro1 the 1 sensitivity. recovery time of thet' receiver, so aster-3 not;0n1y su'ppress the, transmitted pulse from the. V. scre'enfof thevisual display unit of the receiver; but"a1so;to;suppress "subsequent noise or hashl. due to' super regenerative detection radiation: 7

Afstill further object in providingthi'svariable? receiver-sensitivity control" or suppression circuit. is to make available a suppressionpmse waves; formi hav an pQnntial form'of rise. 'foiits'i leading edg'e', the purpose of Whichis toLde'la'y the time atwhich' difierentiation. of the; suppression The 1-system" herein described 'is particularly 1,50

adapted fo'rj use 1mginterrogatoramispanaer j responser radibi ,de'vices ponu ail "referred; .to IFF, OrYIdentification,Friendlor Foeli Thes devices include a pulsed waveimtermgawr bias local IFF set, ,which transmits'hedefi 'polse'radio" freqnencywaveswhich;f,whenv 'piekeddi bi a re ceiver iini gtlie transponder ,lpdrtion j of, .a distant; IFFC'setfi trigger answering ;jcoded 'pulselu waves Ll; which are automatically gtr'ansmittedby a Manse mitter' in thejtransponderuportion ofith' re rn'iit 1T IFFJset Vdue to: trigg ringQarrangerfimQ incor porated; The; iansweriri'gmcodett pulse; waves a'mi; receivediin'fthejtrespohsergofithJocaLIEFlTsetI V The receiver in the transponder isjof .jth Stine regenerative. 7 type. and... considerable; noise; hja'shff is developed .whi'ch,. whenltranslatedgo 1-1 the screen of fthecathodegray Ltubel. oscilloscope, forming'ja ipart Lot the responser,..b1urs outline-L answering signakfr'omthe remoteitransriondento the point bf uninte ll'i'g'ibility fiiItifisllt'er yidesirabl L1 however to use, a superregenerativi .ree'itker 4 the transponder. ,because-ofrits hhighlsensiti'iiit lackof .selectivityg and.adaiitabilityitdl ra'pidtunr:

Itisani obj ejct oi thwpres'entinilention to-"bride; 7 vide a bldckingjsigriaitolth'stiperheterddyfie re; ceiver 'of the, local;ltr'ansponder whichstarts at the instant *of "transmissiontbfgithliloeai.Qinte rogator pulseiandjla'stsbnly; long; enough lforithe answering' signals from remote transponders l,t o bereceived in thelocal responseiz. ,By this the'local transmnde noes. murmmemmtii their. local interrogatorresponser. blit yetfisilins'tant available foriresponselto anointerrogationnfro a remoteiIFF exceptidiiring ,.a v'e" brief/intervals, followingteach1transmittediaulsev thiloeallin terrogatori and "embraeing ih interns same;- spQnSer'cyqIejofjoperationm v While the circuits andLdei/icsiare aescr' eassigg being adapted "for use in this'ty'pe 'of transmitter and receiver, it isto be-vunderstoodflthat the use is not limited thereto, but maybe ezitended gener; ally to various'*e1eetronie receiversand"deitices' The"suppressorsystemfhreifii described be termed a -bia s'ed type, multivibrator'j whl when actuated by "the" leadingl gedge "of wcan.iiiipiit triggering pulse: furnishes an output; .iyolta ge-E wiilifthat' is,-;the output' inipexiahceioiflfi multls vibrator'network'serves asithesresistance som ponent of a resistance-capacitance integrating circuit. The output voltage of the system is exponential in that the voltage charges the condenser in the input circuit to which it is applied with a constantly increasing amplitude over the period determined by the output of the device. This results in the immediate application of said amplitude rise to the circuit for the time of the exponential rise, which, in effect, postpones the differentiating action until the maximum of the voltage output is reached.

Whereas differentiation of the pulse commonly occurs at 'thepeak voltage with no prolongation of its time factor in present equipments, the present device adds to the diiferentiation curve of the pulse a much longer time element of duration by adding the exponential rise period.

In the drawings, wherein like numerals denote like parts,

Figure 1 is a schematic View of the novel circuit as applied to the capacitive input of a suppression pulse amplifier circuit;

Figure 2 is a graphic representation of the variable square wave type pulse applied to the circuit of Figure 1, and also the output Waveform whefinotapplied toa capacitive circuit;

Figure 3is'a graphic representation of one output waveform obtained from the circuit shown in Figure 1 when loaded; I

Figure4'is a schematic-diagrammatic View of the screen of the cathoderay tubeoscilloscope of a receiver'used in transponder, radio equipment; this illustrates an ineffective suppression pulse starting, in time relationship, prior to the initia: tion of the screen sweep, and the hash, as it appears after the rectangular pulse, from the hitherto low impedance source, has'difierentiated to a value which allows premature sensitivity recovery of the receiver.

Figure 5 is a similar view to that of Figure 4, diagrammatically illustrating noise, premature recovery, and'the differentiation curve of a nonextended suppressor pulse, showing how the pulse begins to difierentiate'as'soon as its amplitude has reached maximum. u

Figure 6 is a similar view' of the screen of Figure 5 diagrammatically illustrating integration and differentiation j curves of a delayed blanking pulse produced by the invention herein described, and further illustrating the absence of noise indicationsover the full face ofthe screen.

Figure 7 is a schematic partial diagram of a diode-input, network of a suppressor amplifier circuit to' which the output of the multivibrator may be applied;

Figure 8 is a block plan diagrammatic view of parts of interrogator-transponder-receivers as used in airplanes during Friend orFoe interrogation, and illustrating the path of emission of the suppressor pulse and interrogating pulse.

It is to be noted in Figures 4, 5 and '6 that the suppression pulse; exponential rise (or integration) and differentiation curves shown will never appear on the cathode ray tube screen.

Suppressor operation Referring to the drawings in Figurel, the input to the suppressor I4 is a positive rectangular pulse through contact l0 and into a capacitor H and then through variable resistor l 2 whichserves as an attenuatorfor the input pulse. The pulse then is applied to the grid l3 of the left hand triode of the dual triode vacuum tube M which forms a multi-vibrator of theslf-biased type. For the purpose of describing the'triggering action of this multivibrator, let us assume that the left hand triode l5 normally has its plate current out 01f due to current resulting from conduction of right hand triode 18. When the triggering pulse. arrives on grid 13, plate current is increased due to the conduction caused by the trigger pulse. This lowers the plate voltage on plate 16 and causes the leading edge of the negative pulse from the plate, applied through capacitor I! to the grid of the right hand triode 18, which is normally in a conducting state, to bias this right hand triode [8 to plate current cut-off condition. This cutting off of conductance of right hand triode I8 leaves capacitor I? with a negative charge. This charge is continuously applied to the grid [8 of the right hand triode until the voltage on capacitor I! has been lowered by discharge, through the variable resistor 19 and common cathode resistor 20, to the point where the right hand triode Hi can again assume its conductive state. When triode [8 again assumes its conductive state, plate current flowing through cathode resistor 20 causes triode IE to again assume its original cutor: condition, wherein it is ready to be again triggered by a successive suppression triggering pulse.

The new wave form taken from across plate load resistor 2 I, is a rectangular pulse of variable width. This width is controllable by the adjusted value of resistor l9 and is applied through an attenuator consisting of capacitor 22 and potenti ometer 23. The output circuit, therefore, is of high impedance since it is taken from the plate circuit and, when applied to a capacitive input circuit; will charge the capacity of the input cir- "cuit, the voltage rise being exponential in form and diagrammatically indicated at Figure 3.

is of variable width and of low impedance. 'In

eifect, the multivibrator circuit described may thereby serve as an impedance matching device.

. In order to describe the operation of the suppressor, a complete dual systemis illustrated in Figure 8 as applied to two airplanes A and B.

As airplane A interrogates airplane B, a pulse, starting in time prior to the start of the final interrogation output pulse of the interrogation-responser installation on airplane A, is generated in the interrogator-responser modulator system of airplane A. The interrogating pulse is propagated from antenna 26 of airplane A. The pulse generated for suppression purposes is fed through feed line 27 to the transponder installation 28 in airplane A whichis causing the 'super-regenerative hash radiation, thus preventing recognition of the coded IFF signal which will be sent out from the transponder 29 of airplane B in response to the above interrogation.

Formerly, the sensitivity of the transponder re-.

ceiver had been suppressed only as shown in Figures 4 and'5, by a rectangular, steep-sided pulse from the low output impedance source of a suppressor pulse signal available at the interrogatorresponser. This, because of the low impedance of the output and the capacitive nature of the input circuit of the suppression amplifier circuit of the transponder, caused initiation of differena t i r pulse,tqs hemultiv mt r in the s p- 10.

pressor 49, the output of Mlbeing fed to theame. plifier .45f and receiver portion 35 of transponder 28. The suppressor pulse is first used to trigger the multivibrator circuit andthe output of the multivibrator is applied 'to the suppression aml.

plifiercircuit 45in the- 'transponder 2B, and im mediately begins to depress the sensitivity 'of thetransponder receiver section 35. This eliminates the super-regenerative hash from the interrogator-responser indicating unit 32 since the interrogator-responser receiver 35 in the transponder 28 cannot function While suppressed. Meanwhile, interrogating pulse energy from antenna 2B of airplane A reaches the transponder antenna 36 on airplane B, is detected by its receiver 3! and triggers off transponder transmitter 38 of airplane B in some special IFF code. This IFF signal is propagated from the same transponder antenna 36 and is received at the interrogator-responser antenna 39 of As receiver 40 where it is detected and finally applied to oscilloscope indicator 32. Thus As receiver is suppressed while its other receiver is receiving the desired signal from the transmitter of Bs transponder 38.

From the description of the circuit, it is to be noted that the capacitor ll serves to store pulse voltage and that by varying the value of resistance presented by potentiometer IS, the retention of this stored voltage may be prolonged or short- 40 ened at will, thus delaying or hastening the ensuing resumption of the original or quiescent state of the multivibrator which completes the cycle and forms the trailing edge of the output pulse of the subject device. This delay, occasioned by capacitor l1 and potentiometer I9, results in extending the width or duration of the output pulse from the multivibrator.

When the pulse from the plate outlet 24 is impressed on the input of the transponder suppression amplifier circuit (Figure 7), the transponder receiver 35, which receives the output of the suppression circuit 45, as well as the interrogation signal of airplane B intercepted by its antenna 4|, is cut ofi; that is, its sensitivity is depressed for not only the period of difierentiation of the voltage on capacitor 43 of Figure 7, but also during the period of its charging, as selected by potentiometer 19 of Figure 1.

This duration of charging and discharging of condenser 11 is made long enough to effectively obliterate from the screen 42 of oscilloscope 32 not only the initial transmitted pulse, but also ensuing hash, so that the automatically triggered answering IFF signals'from the transponder 29 in airplane B may be observed. By properly setting potentiometer is, the suppressor pulse may suppress the receiver for 1200 microseconds, as shown in Figure 6, or more, insteadof the heretofore 200 microseconds. As the interrogator-responser cycle of operation is well within 1200 microseconds it is seen that means have been provided for suppressing the transponder during this cycle and for restoring the transponder to operative condition immediately upon comsuppressed during the exponential time ,of riser plus,the small -portion -available during time of differentiatiomas shown'in Figure 6.

From the description of, the circuit, it is to be further notedthat the capacitor ll servesto delay integration or storage of ,thejpulse' voltageduring the alternate triggering actionsof the triodes, and that theresistance of potentiometer l9 may be varied to increase or decrease the dise hfilg B gte atwil wh in' f u h platev Quflet s... m r ss si n e suppression amplifier input circuit of a receiver, such as an lFF transponder system, the receiver is cut off during not only the period of differentiation or discharge of condenser 43, but also during its period of integration or charging. This extra pulse duration which is the sum of charging and discharging time efiectively obliterates from the screen not only the transmitted pulse, but also the ensuing hash so that no noise or hash indications are visible thereon. If only the difierentiation or discharge time were used, all of the hash could not be so obliterated, but only a small portion due to voltage of the difierentiation curve, as shown in Figure 5. By the use of the pulse extender herein described, it has been found possible to extend the noise blanking period clear off the screen, whereas heretofore the most that could be attained was about 10 per cent blanking.

In actual practice the input circuit to suppressor amplifier 45 is as shown in Fig. '7, there being a small capacitor 43 in series in the input. In order therefore to pass the long blanking signal from suppressor 44 it is necessary to make the output impedance of suppressor 44 a high resistance.

The invention has been described in its preferred embodiment and it is contemplated that changes may be made in the details and applications thereof within the spirit and scope of the appended claims.

Having thus described the invention, what is claimed is:

1. An electrical circuit for blanking a receiver, including: a source of blanking pulses; a blanking amplifier having a capacitative input circuit and an output circuit coupled to said receiver to apply a blanking voltage thereto; a self-biased multivibrator triggered by said blanking pulses, the output of said multivibrator being applied to the input capacitative circuit of said blanking amplifier, said multivibrator being adapted to produce output pulses each having a greater time duration than each of said blanking pulses; and means for shaping said output pulses of said multivibrator so that their leading edges gradually rise in an exponential manner.

2. In combination, an interrogator-responser including a modulator; a, transponder including a receiver; and an electrical circuit triggered by blanking pulses derived from said modulator, for blanking said receiver, said circuit comprising: a blanking amplifier having a capacitative input circuit and an output circuit coupled to said receiver to apply a blanking voltage thereto; a selfbiased. multivibrator triggered by said blanking pulses, the output of said multivibrator being applied to the input circuit of said blanking amplifier, said multiyibrator being adapted to produce output pulses eachhaving a, greater time. durationexponential manner.

HOW RD c. STORCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,132,599 Baumann Get. 11, 1938 Luck Aug. 12, 1941 Number Name Date 2,262,838 Deloraine et a1. -2-.. Nov. 18, 1941 2,321,698 Nolde 1 June 15, 1943 2,324,314 Michel July 13, 1943 2,371,988 Granqvist Mar. 20, 1945 2,373,145 Sensiper et al Apr, 10,1945 2,416,328 Labin Feb, 25, 1947 2,540,087 Barchok et a1. Feb. 6, 1951 FOREIGN PATENTS Number Country Date 113,233 Australia June 2, 1941 OTHER REFERENCES .Review of Scientific Instruments, December, 1936 pp. 450-453. 

